Tizen is a software platform (or operating system) compatible with a range of devices (like mobile devices, tablets, smart TVs, in-vehicle devices). The application environment is based on jQuery and jQuery Mobile, allowing developers to use HTML5 and other web technologies.
The project resides within the Linux Foundation and is governed by a Technical Steering Group (with Intel and Samsung in the primary decision-making body).
I have extracted a description from the official site - https://www.tizen.org/:
Tizen is an open source, standards-based software platform supported by leading mobile operators, device manufacturers, and silicon suppliers for multiple device categories such as smartphones, tablets, netbooks, in-vehicle infotainment devices, and smart TVs. Tizen offers an innovative operating system, applications, and a user experience that consumers can take from device to device.
The Tizen project resides within the Linux Foundation and is governed by a Technical Steering Group. The Technical Steering Group is the primary decision-making body for the open source project, with a focus on platform development and delivery, along with the formation of working groups to support device verticals.
The Tizen Association has been formed to guide the industry role of Tizen, including gathering of requirements, identification and facilitation of service models, and overall industry marketing and education.
Tizen provides a robust and flexible environment for application developers, based on HTML5. With HTML5's robust capabilities and cross platform flexibility, it is rapidly becoming the preferred development environment for mobile apps and services. The Tizen SDK and API allow developers to use HTML5 and related web technologies to write applications that run across multiple device segments.
Even thou I'm a happy Android user, having another OS option for mobile devices is always good (I think all Linux users can relate to that).
If you would like to know more about Tizen, take a look at the links and video below.